my gas boiler pumped system is creating air bubbles which are pumpe
around the system and collect in the same 3 rads making them cooler an inefficient. I have to continually bleed them. Is there a systemo pipework fault. Is it to do with venting the system any ideas welcomed. The system was put in my 1930's house by th previous owner
-- mitch
The message from mitch contains these words:
Air isn't created, it has to come from somewhere. When you refill a system you will take in air disolved in the water but this will bleed off in time and any further air introduced during bleeding will progressively reduce.
ISTM that the most likely source of significant quantities of air are either pumping over (pump pressure expelling water into the header tank via the vent) or sucking in air through valve glands if any part of the circuit on the suck side of the pump is below atmospheric pressure. Both these could be construed as design faults.
Pumping over is easy to find - just go and watch the header tank when the system is in operation or even look for a suspiciously warm header tank.
Sucking air in rather harder to diagnose. You need in the first instance to know the head your pump delivers and whether this is at any point greater than the static head anywhere on the circuit. If it is you then need to establish where the feed from the header tank joins the circulating system (which determines the absolute pressure at that point and thus the reference pressure for the whole circuit) and then see whether there is anywhere near the suck side of the pump that could be the culprit.
Figures are available to calculate the losses in the pipework quite accurately but for a first approximation take the ratio of distance to pump to the length of the (shortest) circuit as a whole as a guide. The pump head will give you the pressure difference across the pump which in the first instance can be considered as dissipated evenly round the circuit. The distances from the pump to the header tank feed and to possible entry points, the length of the circuit and the direction the pump pumps should be enough to rule any possible entry point in or out.
Air will diffuse in through any leaks even if the water is well above atmospheric pressure. It will do this until the partial pressure of dissolved air in the water is atmospheric pressure, but as the water is continuously heated and cooled, the partial pressure of air will nearly always be below atmospheric pressure when the system cools down, allowing air to leak in even when the water pressure is high.
The other option is that it's not air at all, but gasses produced due to corrosion in the system, due to no/insufficient inhibitor.
Are you sure that it *is* air?
If your system has no inhibitor in it, it could be hydrogen caused by corrosion. You can test this by bleeding a radiator and holding a lighted match in the stream of "air" coming out. If it's hydrogen, it will burn.
If it *is* hydrogen, your system needs a good flush out, followed by refilling and adding a suitable quantity of corrosion inhibitor.
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